What to do: 1. Vaccines - stay up to date 2. Rapid tests (RAT)
- if you are symptomatic (even negative RAT), assume you have COVID
- use RAT to confirm you are +
- once symptoms resolve, use test-to-exit:
- best 2 neg. RAT on 2 days
- at least 1 neg. RAT if you can't
2/6
3. Masks - wear respirators as much as possible (N95, KN95, KF94 or equivalent). If you can't get one, use a surgical mask with knot & tuck, but it's an inferior option.
4. Clean the air: (always do this, but if there's COVID, go all out)
- go outside
-open windows...
3/6
...In the winter, at least crack open. Otherwise, use fans in the windows to increase circulation.
- run HEPA filters or #corsirosenthalbox . Best place is the room you're in. The more the merrier.
- run exhaust fans if windows are open.
4/6
- put a Filtrete 1900 filter in your furnace and run it all the time
- if it's dry, run humidifiers to keep relative humidity at 40%. Especially bedrooms.
6. If you are sharing rooms (like washroom or dining room), especially without masks, clean the air + wait to air it out between uses. And close the lid before you flush!
If you know how it spreads, you know how to stop it.
Exposure is inevitable, infection isn't.
6/6
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You have a bunch of people working in your house. You are super cautious and don't want to take any chances, so you put on your N95, HEPA filters and open windows while they are there. Once they leave, how long do you have to continue this for?
1/6
Step 1 - determine how many air changes you need. ASHRAE recommends 3 air changes = 95% reduction in virus particles. If you're more cautious, then go for 5 air changes = 99.3% reduction in virus particles. You can do more, but the benefit is minimal. ashrae.org/technical-reso…
2/6
Step 2 - determine the volume of the place you want to flush. Houses usually have 8' ceilings. You can measure it out.
Step 3 - determine the clean air delivery rate (CADR). For a CR box on low, it's 275 CFM. Blast it on high and you'll get 425 CFM.
3/6
Comparing Electronic Air Cleaning Equipment and HEPA Filters
Electronic air cleaning equipment producers make claims like 99.9% reduction of contaminants in 60 minutes. What does that mean? How does it compare to stand-alone HEPA filters?
1/10
This is inspired by an article that just came out in April 2022 ASHRAE journal by Stephens et al where they used regressions for comparing them. I'm going to derive a formula here.
But first, what are we comparing?
HEPA filters use passive or subtractive cleaning.
2/10
They remove particles from air that passes through them and deliver clean, particle-free air.
The electronic air cleaners discussed here do not provide clean air. They are active or additive cleaners and they put ions, hydroxyl radicals or other particles into the air.
As time goes on, filters become dirtier and restrict the airflow.
This leads to less ventilation to the space, so changing the filters more often makes sense.
2/8
Changing filters more often is also simple. It doesn't require any serious planning, investments, structural changes, new equipment...it's just updating the frequency of something you are doing already. It's extra business for maintenance companies so they'll recommend it.
3/8
There are concerns about effects of wind, pressurization and HVAC system effects by opening windows.
What do they think will happen? The building will collapse and then explode and everyone will die of CO poisoning from open windows? It's a stupid window.
1/4
This applies to most places like classrooms, offices and stores. It's different for clean rooms or quarantine facilities where very careful airflow is needed.
Also, opening the door as well helps everything air out much faster.
2/4
It uses up more energy when more outdoor air comes in. That's part of ventilation. It doesn't mean you shouldn't be breathing in clean air.
If it is dangerous to open a window, you shouldn't be able to open it.
3/4
The poor air is coming from somewhere - it can be one of two places. When the ventilation comes on, some of the air is recirculated from the space and resupplied and some of the air comes from outdoors.
If the poor air is recirculated, that means that there is another room where the poor air is coming from and that's being supplied into your space. This can be exacerbated if there isn't sufficient outdoor air.
2/4
The other alternative is there is a source of poor air from the outdoor intake. I've seen intakes in old buildings next to parking lots, so car exhaust could be supplied to the rooms. At an old building I worked at, they violated the building code during roof construction...
3/4
The mixed air dampers/economizer are dampers that modulate to select between supplying return air or outdoor air. When they are fully "closed", it's 100% return air and 0% outdoor air. When they are "open", it's 0% return air and 100% outdoor air.
Dampers are designed to fail in the "closed" position - no outdoor air. Why? This protects the equipment and the people in the space. Bringing in 100% outdoor air can damage the equipment and freeze or overheat the occupants.